- 學位論文
GABA抑制血小板凝集作用之機轉探討
Mechanisms involved in the antiplatelet activity of GABA
摘要
GABA(γ-aminobutyric acid) 為一種神經傳導物質，其化學構造是胺基酸類，主要存在於哺乳類的中樞神經系統。當GABA接上細胞的GABA 受體後，會打開氯離子通道，因此抑制動作電位的形成。有研究指出在血小板內可能有GABA的存在，但是關於GABA對於血小板功能的影響仍未被明確的探討，因此本篇研究主要是想探討GABA對於血小板活化過程的影響以及其訊息傳遞方面的抑制機轉。而由本研究的實驗結果顯示，利用免疫金標記染色技術可以証實GABA存在於血小板中，且主要分布於細胞質中。GABA在低濃度時(0.5-1 ?嵱)，對於由collagen引起的人類血小板凝集反應及ATP的釋放會有抑制的作用。GABA (0.5和1?n?嵱)可以抑制由collagen所引起PLC??2的磷酸化及Akt的磷酸化；而對於p38 MAPK、ERK1/2及JNK1/2的磷酸化，GABA (0.5和1?n?嵱)也會有抑制的作用。而不論是由collagen或是PDBu所刺激的47kDa蛋白質磷酸化都可以被GABA (0.5和1?n?嵱)所抑制。此外，GABA (0.5和1?n?嵱)會增加vasodilator -stimulated phosphoprotein的磷酸化。由以上的實驗結果，GABA抑制collagen誘發的血小板凝集可能會涉及下列路徑：GABA會經由PLC??2-PKC來抑制血小板的活化；GABA也會抑制由collagen所引起的MAPKs及Akt磷酸化，最後抑制血小板的凝集反應。另外，GABA可能藉由影響血小板內cyclic AMP的含量，而促進VASP的磷酸化，進而抑制血小板的活性。
並列摘要
γ-aminobutyric acid(GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system and chemically it is an amino acid. In human, GABA acts at inhibitory synapses in the brain by binding to GABA receptors. This binding causes the opening of chloride ion channels to allow the flow of negatively charged chloride ions into the cell. Recent studies have shown that GABA can be found in human platelets. However, the mechanisms involved in the effect on platelet activity of GABA are still unclear, and we are interested in investigating its effect on cellular signal transduction during the process of platelet activation. In this study, we examined the intra-platelet GABA distribution using a gold labeling technique and noted that GABA was predominantly localized in the cytoplasm of resting platelets. GABA (0.5-1 ?嵱) exhibited more-potent activity of inhibiting platelet aggregation stimulated by collagen than other agonists (i.e., thrombin). We also found that GABA (0.5-1 ?嵱) can inhibit PLCγ2 activity and Akt phosphorylation stimulated by collagen (1 ?慊/ml). Moreover, GABA (0.5 and 1 ?嵱) was found to significantly inhibit 47kDa proteins phosphorylation induced by collagen (1 ?慊/ml) and PDBu (150 nM). In addition, GABA (0.5-1 ?嵱) inhibited collagen (1 ?慊/ml) induced phosphorylation of p38 MAPK, ERK1/2 and JNK1/2. On the other hand, GABA (0.5 and 1 ?嵱) can also induce vasodilator-stimulated phosphoprotein phosphorylation. In conclusion, our study suggested for the first time that inhibitory effect of GABA in platelet activation may involve in the following: GABA may regulate the PLCγ2-PKC pathway to inhibit platelet aggregation. GABA also inhibited MAPKs and Akt phosphorylaion. On the other hand, GABA may involve in increasing of cyclic AMP, followed by triggered VASP phosphorylation, and finally inhibited platelet aggregation. These results imply that GABA not only has inhibitory action on neurons, but has anti-platelet activity. GABA may be used as an effective tool in treating pathological disorder associated with platelet hyperaggregability clinically.